JPH0580835B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an electronic circuit using a superconducting element,
In particular, it relates to switching circuits using Josephson devices.

[Background of the invention]

Switching circuits using Josephson devices are well known in the art and are typified by quantum interference type circuits, direct-coupled type circuits, and the like. A quantum interference circuit is a switching circuit constructed using a superconducting loop containing two or more Josephson junctions, and its details can be found in IBM Research and Developmet.
Vol. 24, No. 2 (1980). Direct-coupled circuits are non-quantum interference circuits that inject current into Josephson junctions, and a typical example is the DCL circuit. DCL circuit is IEDM Tech.Digest
(1979). These conventional switching circuits using Josephson devices have a drawback that the circuit gain is as small as about 2. Furthermore, since a bias current is constantly flowing through the circuit, approximately 1 to 10 μW of power is consumed per circuit. The Josephson device is a device that operates at cryogenic temperatures and is typically immersed in liquid helium. Compared to the heat of evaporation of liquid helium, the amount of heat generated is large when the power consumption per circuit is 1 to 10μW.
Circuits using Josephson devices according to the prior art have the disadvantage that it is difficult to create logic circuits and systems with a large degree of integration.

DCFP (DC Flux Parametron) is used as a high gain and low power consumption circuit that avoids the drawbacks of these conventional circuits using Josephson devices.
There is a circuit. Regarding the principles of DCFP circuits, Goto et al.
Electronics" (March 16, 1981). The DCFP circuit is a circuit composed of a Josephson junction and an inductor. Therefore, in a DCFP circuit, the circuit is composed of a Josephson junction's junction capacitance and an inductor. The drawback was that oscillation caused by the resonant circuit caused circuit errors.

[Purpose of the invention]

An object of the present invention is to provide a DCFP circuit that suppresses resonance phenomena and operates stably without causing malfunctions. Another object of the present invention is to provide a high gain DCFP circuit that operates stably even with very small input signals.

[Summary of the invention]

To achieve this objective, the present invention inserts a damping resistor in the DCFP circuit to suppress resonance.

[Embodiments of the invention]

FIG. 1 is a diagram showing the principle configuration of a DCFP circuit.
The DCFP circuit includes a first Josephson junction 101, a first excitation inductor 103a, and a load inductor 1.
05, a second Josephson junction 102, a second excitation inductor 104a, and a load inductor 105. The first and second superconducting loops share the load inductor 105 and influence each other via the load inductor 105, so the DCFP circuit has a bistable circuit type with positive feedback. The power inductor 103 is connected to the first and second excitation inductors 103a and 104a through transformer couplings 103 and 104, respectively.
b, 104b. The transformer coupling 103, 1 is caused by the power current supplied from the power line 107 and flowing through the power inductors 103b, 104b.
The DCFP circuit is driven through 04. An input signal line 108 is coupled to some or all of the load inductors 105 via a transformer coupling 106 . The operation of the DCFP circuit will be briefly explained below. When a minute input signal current I _S is input to the DCFP circuit via the input signal line 108 , a minute current I' _S corresponding to the input signal current flows through the transformer coupling 106 to the load inductor 105 . In this state, the power line 107 and the two excitation inductors 103
When the DCFP circuit is driven through a and 104a,
The DCFP circuit transitions to one of the bistable states according to the polarity of the minute input current _IS . That is, the load current I _L flowing through the load inductor 105 is determined by the input minute signal current _IS . Generally the load current I _L
can be larger than the minute input current I _S , and it is theoretically not difficult for a DCFP circuit to have a circuit gain of 10 or more. FIG. 2 is a circuit simulation example of the DCFP circuit shown in FIG. 1. The circuit parameters in the example of FIG. 2 are that the excitation inductors 103a and 104a are
1.8PH, and the load inductor 105 is 5.5PH. The equivalent circuit of Josephson junctions 101 and 102 is the third
A model in which Josephson junction 110, junction capacitance 113, and resistor 112 are connected in parallel, as shown in the figure, was used. The maximum superconducting current of Josephson junction 110 is 50 μA, and the junction capacitance 113 is 1 pF. FIG. 2 shows the currents I P1 and I _P2 flowing through the first and second excitation inductors 103a and _104a of the DCFP circuit, and the load current _IL of the load inductor 105.
In the circuit configuration shown in Figure 1, the first Josephson junction 1
01 junction capacitance and the first excitation inductor 103a
and the load inductor 105 constitute a first resonant circuit, and the second Josephson junction 102, the second excitation inductor 104a, and the load inductor 105 constitute a second resonant circuit. Therefore, when the DCFP circuit switches, an oscillation waveform due to a resonance phenomenon appears in the load current _IL . FIG. 2 shows a state in which the signal oscillates upward relative to the zero level. However, in the DCFP circuit, the minute input signal current I′ _S
flows together with the load current I _L. Therefore, when an oscillation waveform appears in the load current _IL , it becomes an input signal and reverses the polarity of the logic circuit, causing it to malfunction.
In the simulation example shown in FIG. 2, since the oscillation is large, the polarity of the load current I _L is reversed after point A, and a waveform is generated below the zero level. In this respect, a malfunction occurs. In order to prevent such malfunctions, there is a method of increasing the input signal so that the polarity does not change even if oscillation occurs, but this method does not provide a high circuit gain.

FIG. 4 shows a first embodiment of the present invention. In order to suppress resonance phenomena, first and second damping resistors 201 and 202 are connected in parallel to the first and second Josephson junctions 101 and 102. The resistance value of the damping resistor should be selected as a value close to critical damping, that is, R _d √ where L: the sum of the inductance values of the excitation inductor and the load inductor C: the junction capacitance of the Josephson junction. FIG. 5 is a simulation example of the DCFP circuit according to the first embodiment of the present invention.

FIG. 5 shows a case where the resistance value R _d of the damping resistors 201 and 202 is 5Ω. However, for critical braking, R _d is
In the case of 3Ω, a higher resistance value was chosen to speed up the circuit operation. As can be seen by comparing the waveform of FIG. 2, the waveform of FIG. 5 is a pulse waveform in which the oscillation phenomenon due to resonance is suppressed, and no malfunction occurs.

FIG. 6 shows another embodiment according to the present invention.
In the DCFP circuit, the load inductor 105 has a larger inductance value than the excitation inductors 103a and 104a. Therefore, the resonance phenomenon can be suppressed by inserting a damping resistor 301 in parallel with the load inductor and further inserting a damping resistor 302 in parallel with all or part of the excitation inductors 103a and 104a, as shown in FIG. it is obvious.

[Effects of the Invention] According to the present invention, the resonance phenomenon of the DCFP circuit can be suppressed. Therefore, the operation of the DCFP circuit can be stabilized, and the circuit can operate normally even with a very small input signal. This corresponds to increasing the gain of the circuit, which means that the circuit can drive more loads (more fan out).
It is effective in enriching the functions of DCFP circuits and improving the performance of circuit systems.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the principle of the DCFP circuit, Fig. 2 is a diagram showing circuit simulation results of the circuit in Fig. 1, Fig. 3 is an equivalent circuit diagram of a diosephun junction, and Fig. 4 is a first embodiment according to the present invention. FIG. 5 is a circuit diagram showing a circuit simulation result of a DCFP circuit according to the present invention, and FIG. 6 is a circuit diagram of a second embodiment of the present invention. Explanation of symbols, 101, 102... Josephson junction, 103a, 104a... excited inductor,
103, 104...Transformer coupling, 105...Load inductor, 108...Input signal line, 201,
202, 301, 302...damping resistance.

Claims (1)

[Claims] 1 A first superconducting loop consisting of a first Josephson device, a first excitation inductor, and a load inductor, and a second superconducting loop consisting of a second Josephson device, a second excitation inductor, and the load inductor. The switching circuit is characterized in that the one resistor is connected in parallel to the load inductance, and the other resistor is connected in parallel to all or part of the first and second excitation inductors. superconducting switching circuit.